1. Field of the Invention
The present invention relates, in general, to an apparatus and method for regenerating an etchant solution containing metal compounds and, more particularly, to an apparatus and method with which spent etchant solutions containing heavy metals can be regenerated in a semi-permanent manner within the module device without being wasted, so that, in addition to producing no pollution of the environment, it is economically very favorable with an increase in overall etching efficiency.
2. Description of the Prior Art
Corrosion processes, called etching, are usually conducted for the manufacture of semiconductor lead frames, shadow masks, plasma display panels (PDPs), ball grid arrays (BGAs), and printed circuit boards (PCBs). Such etching is generally achieved in etching machines wherein workpieces to be etched are placed on a conveyor and are transported for exposure to an etchant, which is done by, for example, spraying the etchant on them. Examples of commonly used etchant solutions inclued solutions of cupric chloride (CuCl2), aluminum chloride (AlCl3), ferric chloride (FeCl3), nickel chloride (NiCl2), and stannous chloride (SnCl2) in water.
These etchant solutions are very efficient in etching workpieces in the early stage, but gradually decrease in etching vigor and rate with time as shown in FIG. 1 because the etching is based on the continuous reduction of etchant solutions. For example, there is a reduction of ferric (Fe3+) to ferrous (Fe2+) ions, wherein the latter is inferior to the former in etching efficiency. Thus, when the ability of the etchant solution to perform its function is reduced below a critical level, the depleted etchant solution must be totally replaced with a fresh one. Used etchant solutions would be discarded, wholly. In the case of replacing an old etchant solution with a fresh one, a halt of the etching procedure happens during the change, causing a decrease in the overall process efficiency. Additionally, wasted etchant solutions produce serious pollution of the environment because of their high content of various heavy metals. Further, poor etching ability is directly associated with poor quality of the final products. Thus, if there is no means of detecting and compensating for the gradual degradation of ethching efficiency, the final products are increasingly deteriorated in quality, which causes problems for the management of process procedure and product quality.
To overcome the problems mentioned above, there were proposed regenerating methods for etchant solutions in which spent etchant solutions are reoxidized by acid or oxidizers. However, the conventional regenerative approach has proven to be economically unfavorable because it is relatively costly and requires investment in expensive apparatus, which furthermore occupy a very large part of the production space of industrial installations.
U.S. Pat. No. 4,060,097 discloses an etchant regenerating system in which a light sensing means senses the intensity of light rays passing through a sample of the etchant and a constitutent component adding means responsive to the light transmittance is operated to regenerate the etching ability of the etchant composition. This etchant regenerating system ensures a regeneration effect but only if the etchant solution contains one kind of metal. When some impurities are fed into the etchant regenerating system, its function may be disturbed. For example, water, if added to the etchant solution, increases the light transmittance, making it difficult for the light transmitting method to restore the etching ability of the etchant solution. Further, when impurities generated in the previous process flow back to the etchant solultion, the light sensing means cannot recognize the degeneration of the etching ability. In addition, when added to the spent etching solution, an excess of a necessary oxidizer upsets the reaction balance of the solution such that the etching vigor is weakened, but the conventional regenerating system dependent only on a light transmission principle lacks the ability to detect this problem and thus, is limited in its ability to accurately monitor the status of the etchant. Another problem occurs with the conventional etchant regenerating system where a combination of various kinds of metals, such as an alloy, is etched. Because the constituent metal components of the alloy express their own colors in the etchant solution used, the etching vigor of the etchant solution varies irrespective of the light transmittance. Thus, the conventional etchant regenerating system cannot restore the etching ability of the etchant solution with accuracy. In fact, in the event that alloy 42 (Fe 58%+Ni 42%, trace amounts of Si, Mg, etc), which is use for a semiconductor lead frame, dissolves in an etchant solution, the etchant regenerating system, in the prior ant, cannot monitor the ethching ability of the etchant solution, but aggravates it.
It is an object of the present invention to overcome the above problems encountered in prior arts and to provide an apparatus and method for regenerating an etchant solution, in which the used etchant solution is regenerated within the module device without being wasted, thereby reducing the etching cost and producing no pollution of the environment.
It is another object of the present invention to provide an apparatus and method for regenerating an etchant solution, which can keep the etchant solution, if it contains metal compounds, at a constant level, thereby increasing the workability and economic profit as well as improving the product quality.
In accordance with an embodiment of the present invention, there is provided an apparatus for regenerating an etchant solution containing a metal compound, comprising: a circulating means for circulating a sample of etchant from a reservoir along a flow path; an additive solution adding means responsive to the instruction of a microprocessor for selectively adding one of additive solutions containing acid and/or oxidizers to the etchant solution in the reservoir; a microprocessor for analyzing etchant color data transmitted from the following color sensors in comparison to the ideal color patterns and for activating the additive solution adding means to select and add a specific additive solution in response to the analyzed result; a first color sensor for sensing the color condition of the etchant by radiating a certain wavelength of light through the influent etchant sample from the reservoir and detecting the diffused light and for transmitting the color data to the microprocessor; and a second color sensor downstream of the additive solution adding means for sensing the color condition of the controlled etchant to determine whether the etchant has been regenerated to increase its vigor as an etchant and for transmitting the color data to the microprocessor.
In accordance with another embodiment of the present invention, there is provided a method for regenerating an etchant solution comprising metal compounds by selectively adding additive solutions containing acid or oxidizers to the etchant solution when the etching ability of the etchant solution is determined to be lower than a predetermined value as a result of the monitoring of a sample of the etchant solution, comprising the steps of: analyzing the sample for the intrinsic color of the etchant solution with a color sensor and transmitting color data to a microprocessor from the color sensor, said color data being made and digitalized by the color sensor; comparing the color data of the etchant solution input from the first color sensor with pre-tested/measured colorimeter data for metal compounds or alloys; selecting a suitable one of pre-set additive solutions according to the etchant condition analyzed in the previous step and adding the selected one to the etchant solution; and sensing the color condition of the added etchant solution to determine whether the etchant has been regenerated to increase its vigor as an etchant and transmitting the color data to the microprocessor.